Thermal sludge to energy transformer

ABSTRACT

Systems and processes provide for a thermal process to transform sludge (and a variety of other natural waste materials) into electricity. Dewatered sludge and other materials containing a high amount of latent energy are dried into a powdered biofuel using a drying gas produced in the system. The drying gas is recirculated and is heated by the biofuel produced in the system, waste heat (from turbines or internal combustion engines), gas (including natural gas or digester gas) and/or oil. The biofuel is combusted in a boiler system that utilizes a burner operable to burn biofuel and produce heat utilized in a series of heat exchangers that heat the recirculating drying air and steam that powers the turbines for electricity production.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/074,370 filed on Nov. 7, 2013. The contents of theaforementioned application is incorporation by reference herein.

BACKGROUND Field

This application relates generally to processing of waste into energy,specifically the production of electrical and thermal energy fromsemi-solid waste materials containing organic solids and, morespecifically, to processing municipal sewage sludge, agricultural andfood waste, as well as other natural waste materials (hereinafterreferred to as “sludge”) into energy.

Related Art

Sludge management and production of energy without consuming fossil fuelare world-wide issues that can pose significant economic, health, andenvironmental challenges. Sludge is typically disposed of on land; thedegree to which it must be stabilized before this land disposal variessignificantly by jurisdiction. Sludge is known to contain harmfulpathogens and bacteria, and naturally decomposes into methane-containinggasses and compounds containing nitrates and phosphorus; sludge can beboth an environmental and public health problem. Sludge can, however, beviewed as a resource instead of waste because it contains significantlatent energy. This latent energy is also referred to as “calorificvalue” and is measured in BTUs (British Thermal Units). An emergingpractice at wastewater treatment plants is to utilize a portion of theenergy in sludge by capturing and burning portions of themethane-containing gasses that are a byproduct of anaerobic digestion(leaving the remnant, digested sludge, to be managed offsite). As muchas 50 percent of the calorific value in sludge can be released throughanaerobic digestion. Many systems and processes have been developed tosafely and economically manage the sludge that remains at the end of thewastewater treatment process. In general, systems and processes aredesigned to remove moisture from the sludge before it is released intothe environment. The moisture removed from the sludge (referred toherein as “wastewater”) is generally returned to the headworks of thewastewater treatment plant for processing. For the most part the energyin the sludge that remains at the end of the treatment process is anunused resource.

Sludge, regardless of its origin, can be categorized based on thetreatment that it has undergone. For example, sludge that has not yetbeen stabilized through decomposition by anaerobic bacteria is referredto as “undigested sludge,” while sludge that has been decomposed byanaerobic bacteria is referred to as “digested sludge.” Typically,undigested municipal sewage sludge and raw/fresh animal or food stockwaste has a relatively high calorific value, while digested municipalsewage sludge and aged animal or food stock waste typically have lowercalorific value in comparison.

A number of methods have been developed for transforming the latentenergy in sludge into usable energy; some of the methods are combustion,gasification, pyrolysis, and thermal hydration. These methods,historically, reduce rather than eliminate the amount of sludge thatrequires land disposal and will not generate the thermal or electricalenergy needed for the process to run without gird electricity and/orfossil fuel.

Thus, systems and processes for the elimination of sludge that can alsogenerate an adequate amount of electrical and thermal energy to sustainthe process are desired.

SUMMARY

In some examples, a system to produce energy from sludge may include aheater, a dryer with a grinder and/or mill (“Dryer”), a system boiler,and a turbine, or any combination thereof. The Dryer is operable toreceive high-temperature gas and sludge, and reduce the moisture contentof the sludge and break the sludge into a dried powder (referred toherein generally as “biofuel”) in the presence of the high-temperaturegas, wherein the high-temperature gas absorbs at least a portion of themoisture content of the sludge to become at least partially-saturatedgas. The system may include a conveyance for a re-circulating stream ofthe high-temperature gas (“drying gas”) to transform the sludge intobiofuel using heat from one or any combination of the following sources:digester gas or a form of natural gas combusted in a gas-fueled heater,biofuel combusted through a burner within the system boiler, and/orexhaust heat from turbines or internal combustion engines. The systemmay include a first separator operable to separate the biofuel from theat least partially saturated drying gas and either a condenser operableto reduce a moisture content of the at least partially saturated dryinggas by reducing the temperature below the dew point of the at leastpartially saturated gas or a diverter to divert a portion of the atleast saturated drying gas containing the amount of moisture evaporatedfrom the sludge, becoming a reduced-moisture drying gas. The system mayinclude the following components to reheat the reduced-moisture dryinggas into a re-circulating stream of drying gas: the above describedgas-fueled heater, a first primary heat exchanger operable using heatfrom the combusted biofuel, and/or a second primary heat exchangeroperable using exhaust heat from turbines or internal combustionengines. The system may also include: a first fan operable to direct aportion of the re-circulating stream of drying gas heated by thegas-fueled heater to the Dryer, and/or a second fan operable to direct aportion of the circulating stream of drying gas heated in the systemboiler to the Dryer and/or a third fan operable to direct a portion ofthe circulating stream of drying gas heated from the exhaust air to theDryer.

In one exemplary embodiment, portions of heat from the system boiler maybe conveyed to the turbine generator system instead of the Dryer. Athird primary heat exchanger may convey heat from the system boiler tothe turbine generator system and power may be generated for running thesystem and for other uses.

In some examples, the system boiler may include a burner operable toburn a mixture of ambient or preheated air and at least a portion of thebiofuel as fuel. This burner may be further operable to burn an oil orgas, separately or in combination with biofuel.

In some examples, the first condenser may be operable to receive wateror oil at a first temperature, the water or oil to be used to reduce thetemperature of the at least partially saturated drying gas, wherein thefirst condenser may be further operable to output the water or oil at asecond temperature that is higher than the first temperature. The wateror oil at the second temperature can be used for power or combined heatand power (“CHP”) generation or other purposes. In some examples, thesystem may include a storage tank operable to store the water or oilafter being used for power or CHP generation or other purposes, whereinthe first condenser is coupled to receive water or oil from the storagetank, although this water or oil may come from any source and be usedfor any purpose or no purpose.

In some examples, the system boiler's exhaust system includes a secondseparator operable to separate at least a portion of ash byproduct ofthe combustion of the biofuel in the system boiler, wherein the secondseparator is further operable to discharge this ash from the system. Theexhaust system may further include a second condenser operable to reducea moisture content of the combusted air from the system boiler to form areduced temperature combusted gas. The exhaust system may furtherinclude another fan operable to discharge the reduced temperaturecombusted gas to the system pollution control equipment and ultimatelyto the atmosphere.

In other exemplary embodiments, processes and computer-readable storagemediums are provided for processing sludge using the systems describedabove.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a block diagram of an exemplary system fortransforming sludge into energy.

FIG. 2 illustrates a block diagram of another exemplary system fortransforming sludge into energy.

FIG. 3 illustrates a block diagram of another exemplary system fortransforming sludge into energy.

FIG. 4 illustrates an exemplary process block diagram.

FIG. 5 illustrates an exemplary computing system that may be used tocontrol a sludge treatment system.

DETAILED DESCRIPTION

The following description is presented to enable a person of ordinaryskill in the art to make and use the various embodiments. Descriptionsof specific devices, techniques, and applications are provided only asexamples. Various modifications to the examples described herein will bereadily apparent to those of ordinary skill in the art, and the generalprinciples defined herein may be applied to other examples andapplications without departing from the spirit and scope of the variousembodiments. Thus, the various embodiments are not intended to belimited to the examples described herein and shown, but are to beaccorded the scope consistent with the claims.

FIG. 1 illustrates a block diagram of an exemplary treatment system 100.As an overview, treatment system 100 may be used to produce power fromsludge by converting sludge 30 into biofuel that is combusted to produceheat used in the system for the production of both biofuel and power. Intreatment system 100 the drying gas receives its heat from air-airboiler heat exchanger 12 within boiler 11.

Treatment system 100 may include a storage unit 1 for holding sludge 30brought into the system. In some examples, storage unit 1 may be used tostore sludge that has been dewatered to have approximate 40 to 85percent moisture content at ambient temperature (i.e. “dewateredsludge”). However, it should be appreciated that sludge having othercontent ratios may be used. Storage unit 1 may include any type ofstandard storage system suitable for storing sludge. The volume ofstorage unit 1 may depend on the location of treatment system 100 andthe sludge source. For instance, if treatment system 100 is situated ata municipal wastewater treatment plant or large-scale agricultural orfood processing operation with an adequate continuous supply of sludgeand onsite dewatering, storage unit 1 may be used only as a surge binhaving a two to three hour sludge capacity. If, however, the treatmentsystem 100 is at a facility where the supply of sludge is notconsistently available for efficient operation of the system on acontinuous basis, be it at a treatment plant, food processing facility,hog farm, cattle ranch, farm, or dairy with sludge being trucked in fromother sites, storage unit 1 may have a volume allowing storage of a24-hour or more running capacity of dewatered sludge. However, it shouldbe appreciated that, irrespective of the examples cited, a storage unit1 having any desired capacity may be used.

Treatment system 100 may further include a dryer that includes agrinder, and/or mill (or combination thereof), hereinafter referred toas a Dryer 2 in which the moisture may be reduced or removed from thesludge that has been dewatered (either at the treatment site or offsitedewatering equipment of any sort may be included in the system inadvance of the storage unit 1). The Dryer 2 may also be used to processthe dewatered sludge to a uniform, or at least substantially uniform,size (becoming biofuel after drying and processing). The Dryer 2 may beof any design that is able to pulverize the dewatered sludge into a finepowder, e.g., 80% of which would be smaller than 80 microns and can passthrough a #200-sieve screen, and with a moisture content of less thanabout 30 percent. In some examples, Dryer 2 may be of a size operable toprocess on the order of 60 wet tons of dewatered sludge (40%-85%moisture) over a 24-hour period by drying and milling or grinding thedewatered sludge as described above. However, Dryer 2 may be of anygreater or lesser capacity (size) and the system may reduce the moistureof the sludge to any amount.

It should be appreciated that the operating temperature of thehigh-temperature gas at Dryer 2 may vary depending on the specificsludge application. Increasing the temperature of drying gas stream inDryer 2 enables increased moisture pickup per unit weight of sludge. Asa result, the throughput of Dryer 2 for dewatered sludge of anyparticular moisture content may be increased in proportion to heat inputto the Dryer 2. In one example, the drying gas stream coming to theDryer 2 is received at a temperature between 600° F. and 1,500° F. Inthis example, the source of heat for drying gas stream coming to Dryer 2is an air-air boiler heat exchangerunit 12 within system boiler 11. Aswill be described in greater detail below, mixer 27 may divert a portionof the portion of the now cleaned drying gas stream not drawn throughdiverter valve 17 into the drying gas stream exiting air-air boiler heatexchanger 12 in order to produce the drying gas stream of the desiredtemperature for Dryer 2. Due to the evaporative cooling that occurswithin Dryer 2, the temperature of the drying gas stream entering Dryer2 will be reduced before exiting Dryer 2. The drying gas stream enteringDryer 2 absorbs moisture from the sludge and exits as an at leastpartially saturated drying gas stream.

The sludge 30 may be transferred from storage unit 1 to Dryer 2 usingany means that is capable of delivering an accurate, modulated supply ofsludge to the Dryer 2. For example, an auger capable of deliveringpreviously dewatered, but otherwise wet, sludge may be used to supplyDryer 2.

Treatment system 100 may include gas-solids separator 5 for separatingparticulate from the at least partially saturated drying gas streamexiting from Dryer 2. Gas-solids separator 5 may be configured to removethe biofuel from the at least partially saturated drying gas streamcarrying the sludge moisture from Dryer 2. In some examples, thetemperature of the mixture of biofuel and at least partially saturateddrying gas stream from Dryer 2 may be at approximately 300° F. However,it should be appreciated that this temperature can vary depending on thesystem application or design. Gas-solids separator 5 may be configuredto separate the biofuel from the at least partially saturated drying gasstream and deposit the biofuel in a biofuel bin 6. In some examples,gas-solids separator 5 may be made from a material capableofwithstanding high gas temperatures and corrosive materials, such asstainless steel or other appropriate materials, and may be operable toremove at portion of the biofuel from the at least partially saturateddrying gas stream. Separator may also include a fabric-type gas-solidsseparator (baghouse) 28 to separate the remaining solids from the atleast partially saturated drying gas stream.

In some examples, gas-solids separator 5 may be a cellular-typeseparator. In these examples, the inlet to each individual cell may befitted with a multiple blade spinner arranged to spin the at leastpartially saturated drying gas stream and convey the particles to theoutlet of the cell. The particles may, for example, be deposited intobiofuel bin 6 via a rotary valve or any other means (not shown). The atleast partially saturated drying gas stream is at least partiallycleaned by separator 5 and fabric-type gas-solids separator 28 andenters condensing-type scrubber 7 as partially cleaned at leastpartially saturated drying gas stream. The partially cleaned at leastpartially saturated drying gas stream passes through condensing-typescrubber 7 where its moisture content is reduced and exits as a cleaneddrying gas stream.

As mentioned above, once separated from the at least partially saturateddrying gas stream, the biofuel may be sent to biofuel bin 6.Additionally, as described in greater detail below, in some examples,biofuel bin 6 may include an auger that meters the biofuel into a mixbox 8 where it is combined with ambient and/or preheated air and thenused by dual fuel burner 10 and combusted in the system boiler 11. Itshould be appreciated that any delivery rate or biofuel to air mixturemay be used depending on the objectives of the system. In some examples,biofuel bin 6 may include a safety system to prevent dust explosions.The safety system for biofuel bin 6 may reduce the possibility of dustexplosions by, for example, injecting an inert gas, such as nitrogen orcarbon dioxide, into biofuel bin 6.

Treatment system 100 may further incorporate a bottom ash collectionsystem in system boiler 11. The bottom ash collection feature mayfurther gravity feed a separate or integral ash storage bin 21.

Treatment system 100 may further include a process fan 29 to draw avacuum to pull the at least partially saturated drying gas streamthrough gas-solids separators 5 and 28, and condensing-type scrubber 7and to diverter valve 17 in order to divert a portion of the now cleaneddrying gas stream from the drying gas loop through gas-water heatexchanger 15. Heat exchanger 15 cools the diverted portion of cleaneddrying gas stream using process water from an ambient-temperature watersource 32 and condenses out a volume of moisture equal to the moisturecontained in sludge 30 from the diverted portion of cleaned drying gasstream via condenser 14. Prior to reaching condenser 14, heat drawn fromthe diverted portion of the cleaned drying gas stream by gas-water heatexchanger 15 may be used as the source of heat for heating the plantdigesters or other Combined Heat and Power (CHP) out-of-system uses 32(not shown) or for no use. In some examples, process fan 29 and divertervalve 17 may be made from temperature and corrosion-tolerant materials,such as stainless steel or other appropriate materials. Diverter valve17 functions to keep an overall moisture balance in the drying gas loopby diverting a portion of cleaned drying gas stream carrying a volume ofmoisture equal to that absorbed from the sludge less the volume ofmoisture removed by condensing-type scrubber 7.

Treatment system 100 may further include make-up air supply 16 toreplace the amount of the cleaned drying gas stream diverted from thedrying gas loop by diverter valve 17. It should be appreciated thatmake-up air supply 16 may be ambient temperature or preheated.

Make-up air supply 16 may include air supply fan 25. It should beappreciated that make-up air supply 16 can be located before or afterprocess-air circulation fan 4.

As mentioned above, treatment system 100 may further include a condenser14 for condensing moisture from the diverted portion of cleaned dryinggas stream. In some examples, this diverted portion of cleaned dryinggas stream may be at a temperature above its dew point. The shell ofcondenser 14 may be made from a high-temperature and corrosion-tolerantmaterial, such as stainless steel or other appropriate materials. Heatin the diverted portion of the cleaned drying gas stream will betransferred through heat exchanger 15 to process water circulatedthrough heat exchanged 15 using a re-circulating water system (notshown) that will convey the heat to out-of-system uses. The divertedportion of cleaned drying gas stream passing through heat exchanger 15will be conveyed to condenser 14 that will then, utilizing process waterfrom an ambient-temperature water source 33, reduce the temperature ofthe diverted portion of the cleaned drying gas stream to below its dewpoint. The moisture in the diverted portion of cleaned drying gas streammay be recovered by lowering the temperature of this gas stream to belowits dew point by, for example, using the process water from anambient-temperature source, thereby causing the moisture to condense outof the diverted portion of cleaned drying gas stream. As the moisturecondenses into water, it may collect carry-over particulate remaining inthe gas stream and carry the particulate as sludge condensate 34 whichis to be removed from the system and conveyed to the treatment plant orother out-of-system treatment (not shown). A reduced-temperaturediverted portion of cleaned drying gas stream exits condenser 14 and isconveyed to primary air supply inlet 20 at system boiler 11 where itwill be serve as a portion of the combustion air utilized with thebiofuel from biofuel bin 6 and combusted utilizing duel fuel burner 10.Additionally, after the aforementioned process water used to cool thediverted portion of cleaned drying gas stream into condensate, asdescribed above, is warmed and may be either returned toambient-temperature water source 33, or used for any purpose when itexits condenser 14.

Treatment system 100 may further include process-air circulation fan 4for drawing the portion of cleaned drying gas stream fromcondensing-type scrubber 7 that was not diverted by diverter valve 17and circulating it to the air-air boiler heat exchanger unit 12 withinsystem boiler 11. In some examples, process-air circulation fan 4 may bemade from temperature and corrosion-tolerant materials, such asstainless steel or other appropriate materials, and may circulate 100percent of the weight of gas that passes through treatment system 100.Process-air circulation fan 4 may include a speed control that may beadjusted based on the characteristics of the sludge fed to Dryer 2.While shown at the output of condensing-type scrubber 7, it should beappreciated that process-air circulating fan 4 may be combined withprocess fan 29 or located at the output of any of Dryer 2, gas-solidsseparators 5 and 28, or condensing-type scrubber 7.

Treatment system 100 may further include mixer 39 that may divert aportion of the portion of the now cleaned drying gas stream not drawnthrough diverter valve 17 into the drying gas stream exiting air-airboiler heat exchanger 12 in order to produce a drying gas stream of thedesired temperature for Dryer 2. In some examples, mixer 39 may be madefrom temperature and corrosion-tolerant materials, such as stainlesssteel or other appropriate materials, and may divert up to 100 percentof the weight of gas that passes through treatment system 100.

As mentioned above, dual fuel burner 10 will be used to produce heat forDryer 2 operation and/or to produce steam for the steam system/turbine18. The dual fuel burner 10 may utilize any single or a combination ofmultiple fuels. The primary source may be biofuel supplied from biofuelbin 6. The secondary source may be a supplementary fuel 26, such as gas(e.g., digester gas, natural gas, propane, and the like) or oil. Theflow rate of fuel supplied to dual fuel burner 10 may be controlled asdesirable for sludge drying in Dryer 2 and/or to produce power from thesteam system/turbine 18. Additionally, the dual fuel burner 10 may beable to supply up to 100% of the heat required using either biofuel orsupplementary fuel 26 alone. In some examples, dual fuel burner 10 mayinclude separate ignition systems (not shown), which may be fired bybiofuel, oil, or gas. In some examples, the separate ignition burner maybe used to maintain the system temperature in a stand-by mode duringtimes when sludge is not being processed or power production is notdesired.

The steam to power steam system/turbine 18 circulates through turbineair-water heat exchanger 35 located with system boiler 1 lwhere heat istransferred from the combustion of biofuel to the steam. The heatavailable to produce steam for the steam system/turbine 18 is heatremaining after sufficient heat is conveyed to the drying gas stream viaair-air boiler heat exchanger 12.

The dual fuel burner 10 may be supplied with biofuel and air drawnthrough a combustion supply fan 9. In some examples, combustion supplyfan 9 draws ambient-temperature and/or pre-heated air 38 from theatmosphere and the reduced-temperature diverted portion of cleaneddrying gas stream exiting condenser 14. In some embodiments of treatmentsystem 100, a fuel venturi 19 may include a venturi valve arranged tofurther mix the ambient-temperature and/or pre-heated air 38 and thereduced-temperature diverted portion of cleaned drying gas streamexiting condenser 14 from primary air supply inlet 20 with biofuel frombiofuel bin 6. Primary air supply inlet 20 may include an air-air heatexchanger system (not shown) to preheat the air being used with thebiofuel, as well as a filter and grill fitted with an integraladjustable baffle (not shown) to control downstream pressure andminimize dust drawn to dual fuel burner 10. The combustion supply fan 9may include a dust handling fan and may supply the dual fuel burner 10with the mix of ambient temperature and preheated air, and biofuel. Insome examples, combustion supply fan 9 may include a variable speeddrive to control the airflow to dual fuel burner 10 or, alternately,ambient-temperature or preheated air from the primary air supply inlet20 may provide all of the air to the dual fuel burner 10.

In some examples, the weight of ambient-temperature or preheated air(i.e. new air) that enters dual fuel burner 10 through primary airsupply inlet 20 may be equal to approximately three to ten times thatthe weight of air from diverter valve 17 entering dual fuel burner 10.

Treatment system 100 may further include ash separator 22 for receivingthe combusted air exiting from the system boiler 11. The receivedcombusted air may include ash along with some residual moisture fromsystem boiler 11. Ash separator 22 may be used to remove ash from thecombusted air exiting from system boiler 11 and deposit the removed ashin ash storage bin 21 or ash storage 23. In some examples, ash separator22 may include a Stairmand-type high-efficiency cyclone or a fabric-typeseparator to clean the gas received from system boiler 11. Specifically,one or more separators, each made from temperature andcorrosion-resistant materials (e.g., stainless steel), may be used toseparate the particles from the combusted air exiting from system boiler11 and may discharge the solids to ash storage bin 21 or ash storage 23.The cleaned combusted air exiting ash separator 22 may then be sent toterminal air pollution control scrubber 24. While the above exampleswere described using Stairmand-type cyclones, other cyclone separators,a baghouse, or other gas solids separators capable of functioningeffectively and safely in the operating temperatures may be used toclean the combusted air exhaust from the system boiler 11. It should beappreciated that the air pollution control scrubber may have additionalfunctions depending on applicable air quality standards.

The cleaned combusted air exiting ash separator 22 can be directed toterminal air pollution control scrubber 24. Terminal air pollutioncontrol scrubber 24 may be of a type similar or identical tocondensing-type scrubber 7 and may be used to condense moisture out ofthe cleaned combusted air received from ash separator 22. For instance,terminal air pollution control scrubber 24 may direct the cleanedcombusted air received from ash separator 22 over a series of tubes thatare cooled by the flow of water from an ambient-temperature watersource, causing the gas temperature to drop below its dew point. As themoisture condenses into water at air pollution control scrubber 24, itmay collect carry-over particulate remaining in the gas stream and carrythe particulate as sludge condensate which is to be removed from thesystem and conveyed to the treatment plant headworks or other disposalsite (not shown).

Treatment system 100 may further include a terminal fan 43 for drawingthe cleaned combusted air through the ash separator 22 and air pollutioncontrol scrubber 24. The output of terminal fan 43 may be dischargedfrom the system through the discharge stack 34 after the air pollutioncontrol scrubber 24 and then to the atmosphere.

In some examples, the weight of gas that enters treatment system 100from the atmosphere through primary air supply inlet 20 may be equal tothe weight of gas that is removed from the system though the dischargestack 34 to the atmosphere. As a result, a constant weight of gascirculating through the system may be maintained.

FIG. 2 illustrates a block diagram of another exemplary treatment system200.

Treatment system 200 is similar to treatment system 100, with thedifferences discussed in greater detail below. Reference numbers forcomponents of treatment system 200 that are the same as those used forcomponents in treatment system 100 indicate that a similar component maybe used in treatment system 200.

Treatment system 200 may be utilized when a supply of digester gas isavailable to preheat make-up air supply 16. In treatment system 200,dryer heater 3 is added to the system described in treatment system 100and is the primary source of heat for the drying gas stream. As aresult, in treatment system 200, heat conveyed to the drying gas streamfrom the air-air boiler heat exchanger 12, located within system boiler11 is minimized and the heat directed to the turbine air-water heatexchanger 35 is maximized. With more heat supplied to the steamsystem/turbine 18, the production of power is increased in comparison totreatment system 100.

It should be appreciated that, as with treatment system 100, theoperating temperature of the drying gas at Dryer 2 in treatment system200 may vary depending on the specific sludge application. Increasingthe temperature of the drying gas stream in Dryer 2 enables increasedmoisture pickup per unit weight of sludge 30. As a result, thethroughput of Dryer 2 for dewatered sludge of any particular moisturecontent may be increased in proportion to heat input to the Dryer 2. Thedrying gas stream can be at a temperature between 600° F. and 1,500° F.Sources of heat for drying gas stream coming to Dryer 2 may include anair-air boiler heat exchanger unit 12 within system boiler 11 that willsupplement heat produced from digester gas 31 combusted in digester gasburner 13.

In dryer heater 3, digester gas 31 combusted in digester gas burner 13preheats make-up air supply 16. The make-up air supply 16 may includeair supply fan 25 to assist the air flow into Dryer heater 3. Preheatedmake-up air supply 16 is then injected into the drying gas loop. Itshould be appreciated that preheated make-up air supply 16 may beinjected into the drying gas loop either before or after air-air boilerheat exchanger unit 12 within system boiler 11.

FIG. 3 illustrates a block diagram of another exemplary treatment system300. Treatment system 300 may be similar to treatment system 100, withthe differences discussed in greater detail below. Reference numbers forcomponents of treatment system 300 that are the same as those used forcomponents in treatment system 100 indicate that a similar component maybe used in treatment system 300.

Treatment system 300 may be utilized when a supply of high temperatureexhaust air from power generation equipment (not shown) is available tosupport Dryer 2. In treatment system 300, air-air heat exchanger 37 isadded to the system described in treatment system 100 to preheat theportion of cleaned drying gas going to air-air boiler heat exchanger 12that was not drawn through diverter valve 17 and not divert by mixer 39by transferring heat from the high-temperature power generationequipment exhaust system to the now cleaned drying gas stream. As aresult, in treatment system 300, because drying gas conveyed to air-airboiler heat exchanger 12, located within system boiler 11 has beenpreheated using high temperature power generation equipment exhaust airvia air-air heat exchanger 37 heat available for turbine air-water heatexchanger 35 is maximized. With more heat supplied to the steamsystem/turbine 18, the production of power is increased in comparison totreatment system 100.

Treatment system 300 is based on treatment system 100 with the additionof exhaust air manifold line 36 that runs from power generationequipment (not shown) and delivers heated power generation equipmentexhaust air to the air-air heat exchanger 37, to preheat therecirculating drying gas in advance of air-air boiler heat exchanger 12.After passing through the air-air heat exchanger 37, the exhaust airmanifold line 36 delivers the reduced temperature power generationequipment exhaust air to the appropriate power generation air pollutioncontrol equipment (not shown) before it is released to the atmosphere.

It should be appreciated that in addition to the described exemplarysystems 100, 200, and 300 described, additional systems are possibleincluding variations and combinations of the elements and systemsprovided. For example, certain elements may be optionally removed orreplaced, additional elements may be included, and certain elementsdescribed with respect to one system may be advantageously used in othersystems described. For example, condensing-type scrubber 7 may beremoved or additional mixers 39 may be added.

FIG. 4 illustrates an exemplary process 400 for transforming sludge intoenergy. In some examples, process 400 can be performed using a treatmentsystem similar or identical to treatment system 100, 200 or 300.

At block 401, moisture content of dewatered sludge may be reduced toform at least partially saturated drying gas and biofuel with a moisturecontent of less than 30 percent. In some examples, this may be doneusing Dryer 2 as described above. For instance, dewatered sludge may bebroken up in the presence of drying gas to form a powder having amoisture content of less than about 30 percent. The drying gas mayabsorb at least a portion of the moisture contained in the dewateredsludge. In some examples, the dewatered sludge may be heated at Dryer 2,using, for example, drying gas received from dryer heater 3 and/orair-air boiler heat exchanger unit 12 via process-air circulation fan 4and/or process fan 29.

At block 402, the biofuel may be separated from the at least partiallysaturated drying gas generated at block 401. In some examples, this maybe done using gas-solids separators 5 and 28 as described above. Forinstance, gas-solids separators 5 and 28 may be operable to separate thebiofuel from the at least partially saturated drying gas generated byDryer 2 and deposit the separated biofuel into biofuel bin 6. In someexamples, gas-solids separator 5 may be a cellular type separator andmay include one or more Stairmand-type cyclones or other satisfactoryequipment to clean the received at least partially saturated gas.

At block 403, the moisture content of the at least partially saturateddrying gas may be reduced by reducing the temperature of the at leastpartially saturated drying gas to below its dew point to form areduced-moisture gas (i.e., cleaned drying gas) and hot water. In someexamples, the moisture content of the at least partially saturateddrying gas is reduced using condensing-type scrubber 7 to form cleaneddrying gas as described above. For instance, the at least partiallysaturated gas may be passed through a series of tubes that are cooled byambient-temperature water received from an outside source. As the atleast partially saturated drying gas cools below the dew point of thegas moisture, a portion of the moisture condenses out of the gas. As themoisture condenses into water, it may collect carry-over particulateremaining from the drying gas stream and carry the particulate to thetreatment plant or other out-of-system treatment 34.

At block 404 a portion of the reduced-moisture drying gas generated atblock 403 may be diverted to compensate for moisture contained in sludgeentering the system 30. The moisture content of the diverted drying gasstream may be reduced at condenser 14. The reduced-moisture diverted gasstream (i.e., reduced-temperature diverted portion of cleaned drying gasstream described above) is then conveyed to the primary air inlet 20where it is combined with ambient-temperature and/or pre-heated air 38to be the oxygen source for the fuel burner 10.

At block 405, heating of the reduced-moisture drying gas generated atblock 403 may be accomplished in air-air boiler heat exchanger 12 insystem boiler 11. In some examples, based on treatment system 200, thereduced-moisture drying gas is also heated in dryer heater 3 with heatproduced by combusting digester gas 31 in digester gas burner 13. Insome examples, based on treatment system 300, the reduced-moisturedrying gas is preheated using power generation equipment exhaust gas viaair-air boiler heat exchanger 37 before it is heated via air-air boilerheat exchanger 12 in the system boiler 11.

At block 406, biofuel is combusted in system boiler 11 and produces heatfor the drying gas that is utilized in Dryer 2 and heats the steamcirculating through air-water heat exchanger 35 that powers steamsystem/turbine 18.

At block 407, the reduced-moisture drying gas is then recirculated toDryer 2 to reduce the moisture content of the sludge 30.

It should be appreciated that while the blocks of process 400 areprovided in a particular order, the blocks can be performed in otherorders, and some processes may be carried out partially or fully inparallel. Further, process 400 can include all or a portion of theblocks listed above.

Those skilled in the art will recognize that the operations of somevariations may be implemented using hardware, software, firmware, orcombinations thereof, as appropriate. For example, some processes can becarried out using processors or other digital circuitry under thecontrol of software, firmware, or hard-wired logic. (The term “logic”herein refers tofixed hardware, programmable logic and/or an appropriatecombination thereof, as would be recognized by one skilled in the art,to carry out the recited functions.) Software and firmware can be storedon computer-readable storage media. Some other processes can beimplemented using analog circuitry, as is well known to one of ordinaryskill in the art. Additionally, memory or other storage, as well ascommunication components, may be employed in embodiments of theapparatus and methods described herein.

FIG. 5 illustrates a typical computing system 500 that may be employedto carry out processing functionality in some variations of the process.For instance, computer system 500 may be used to control one or moreelements of the exemplary treatment systems described above. Thoseskilled in the relevant art will also recognize how to implement theapparatus and methods described herein using other computer systems orarchitectures. Computing system 500 may represent, for example, adesktop, laptop, or notebook computer, hand-held computing device (PDA,mobile phone, tablet, etc.), mainframe, supercomputer, server, client,or any other type of special or general purpose computing device as maybe desirable or appropriate for a given application or environment.Computing system 500 can include one or more processors, such as aprocessor 501. Processor 501 can be implemented using a general orspecial purpose processing engine such as, for example, a programmablelogic controller, a microprocessor, controller, or other control logic.In this example, processor 501 is connected to a bus 502 or othercommunication medium.

Computing system 500 can also include a main memory 503, preferablyrandom access memory (RAM) or other dynamic memory, for storinginformation and instructions to be executed by processor 501. Mainmemory 503 also may be used for storing temporary variables or otherintermediate information during execution of instructions to be executedby processor 501. Computing system 500 may likewise include a read-onlymemory or other static storage device coupled to bus 502 for storingstatic information and instructions for processor 501.

The computing system 500 may also include information storage Devices504, which may include, for example, a media drive 505. The media drive505 mayinclude a drive or other mechanism to support fixed or removablestorage media, such as a hard disk drive, a floppy disk drive, a USBflash drive, an optical disk drive, a CD or DVD drive (R or RW), orother removable or fixed media drive. Storage media 506 may include, forexample, a hard disk, floppy disk, optical disk, CD or DVD, or otherfixed or removable medium that is read by and written to media drive505. As these examples illustrate, the storage media 506 may include acomputer-readable storage medium having stored there in particularcomputer software or data.

In some variations, information storage Devices 504 may include othersimilar instrumentalities for allowing computer programs or otherinstructions or data to be loaded into computing system 500. Suchinstrumentalities may include, for example, a removable storage unit 507and an interface 508, such as a program cartridge and cartridgeinterface, a removable memory (for example, a flash memory or otherremovable memory module) and memory slot, and other removable storageunits 507 and interfaces 508 that allow software and data to betransferred to computing system 500.

In some variations, computing system 500 can also include acommunications interface 509. Communications interface 509 can be usedto allow software and data to be transferred between computing system500 and external devices. Non-limiting examples of communicationsinterface 509 can include a modem, a network interface (such as anEthernet or other NIC card), a communications port (such as for example,a USB port), a PCMCIA slot and card, a PCI interface, etc. Software anddata transferred via communications interface 509 are in the form ofsignals which can be electronic, electromagnetic, optical, or othersignals capable of being received by communications interface 509. Thesesignals are provided to communications interface 509 via a channel 510.This channel 510 may carry signals (e.g., signals to and from sensors orcontrollers) and may be implemented using a wireless medium, wire orcable, fiber optics, or other communications medium. Some examples of achannel include a phone line, a cellular phone link, an RF link, anetwork interface, a local or wide area network, and othercommunications channels.

The terms “computer program product” and “computer-readable storagemedium” may be used generally to refer to non-transitory storage media,such as, for example, main memory 503 and storage devices 504. These andother forms of computer-readable storage media may be involved inproviding one or more sequences of one or more instructions to processor501 for execution. Such instructions, generally referred to as “computerprogram code” (which may be grouped in the form of computer programs orother groupings), when executed, enable the computing system 500 toperform features or functions of embodiments of the apparatus andmethods, described herein.

In some variations where the elements are implemented using software,the software may be stored in a computer-readable storage medium andloaded into computing system 500 using, for example, removable storagedrive 507 or communications interface 509. The control logic (in thisexample, software instructions or computer program code), when executedby the processor 501, causes the processor 501 to perform the functionsof the apparatus and methods, described herein.

It will be appreciated that, for clarity purposes, the above descriptionhas described embodiments of the apparatus and methods described hereinwith reference to different functional units and processors. However, itwill be apparent that any suitable distribution of functionality betweendifferent functional units, processors, or domains may be used withoutdetracting from the apparatus and methods described herein. For example,functionality illustrated to be performed by separate processors orcontrollers may be performed by the same processor or controller. Hence,references to specific functional units are only to be seen asreferences to suitable means for providing the described functionality,rather than as indicative of a strict logical or physical structure ororganization.

While specific components and configurations are provided above, it willbe appreciated by one of ordinary skill in the art that other componentsvariations may be used. Additionally, although a feature may appear tobe described in connection with a particular embodiment, one skilled inthe art would recognize that various features of the describedembodiments may be combined. Moreover, aspects described in connectionwith an embodiment may stand alone.

Furthermore, although individually listed, a plurality of means,elements, or method steps may be implemented by, for example, a singleunit or processor. Additionally, although individual features may beincluded in different claims, these may possibly be advantageouslycombined, and the inclusion in different claims does not imply that acombination of features is not feasible and/or advantageous. Also, theinclusion of a feature in one category of claims does not imply alimitation to this category, but rather the feature may be equallyapplicable to other claim categories, as appropriate.

What is claimed is:
 1. A system for generating electricity by combustingbiofuel produced from dewatered sludge, the system comprising: a dryeroperable to: receive a drying gas; receive sludge; and reduce themoisture content of the sludge in the presence of the drying gas,wherein the drying gas absorbs at least a portion of the moisturecontent of the sludge and forms a biofuel, reduced moisture powder, andat least partially saturated gas; a boiler system operable to combustthe biofuel to produce at least one of heat for use in the dryer orsteam for a turbine; a first separator operable to separate the biofuelfrom the at least partially saturated gas; a first condenser operable toreduce a moisture content of the at least partially saturated gas byreducing a temperature of the at least partially saturated gas to form areduced-moisture gas; at least one fan operable to direct thereduced-moisture gas to the heat exchanger to form the drying gas, theheat exchanger disposed in the boiler system and to direct thereduced-moister gas to the dryer to reduce the moisture content of thesludge; a diverter valve operable to keep an overall system moisturebalance by removing the volume of reduced-moisture gas out of the systemthat is equivalent to the volume of moisture removed from the sludgeless the amount removed by first condenser; a make-up air supply toreplace reduced-moisture gas diverted out of the system; a series ofheat exchangers incorporated into the boiler system to transfer heat toat least one of the turbine and dryer.
 2. The system of claim 1, whereinthe sludge comprises at least one or a combination of digested sludge,undigested sludge, fresh animal waste, aged animal waste, agriculturalwaste, or food waste.
 3. The system of claim 1, further comprising amixer operable to mix a second portion of reduced-moisture gas with gasheated by the boiler to form the drying gas.
 4. The system of claim 3,wherein the boiler system comprises a burner operable to burn a mixtureof at least one of ambient and pre-heated air and at least a portion ofthe dried powder.
 5. The system of claim 3, wherein the burner isfurther operable to burn a gas or oil.
 6. The system of claim 1, furthercomprising a heater having a gas burner, the heater operable to furtherheat the drying gas heated by the boiler system.
 7. The system of claim1, wherein the reduced-moisture gas is preheated using heat fromcombusted gas before it is heated in the boiler system
 8. A method forproducing electricity from dewatered sludge in a treatment system, themethod comprising: reducing moisture content of a dewatered sludge in adryer by breaking the dewatered sludge into biofuel in the presence of adrying gas, wherein the drying gas absorbs at least a portion of themoisture content of the dewatered sludge to form at least partiallysaturated gas; combusting the biofuel to produce at least one of adrying gas for use in the drying process and steam for use in a turbine;separating the biofuel from the at least partially saturated gas;reducing a moisture content of the at least partially saturated gas byreducing a temperature of the at least partially saturated gas to belowits dew point in order to form a reduced-moisture gas; heating a portionof the reduced-moisture gas to generate the drying gas; andrecirculating at least a portion of the drying gas by directing it tothe dryer, wherein upon exiting the dryer it becomes partially saturatedgas.
 9. The method of claim 8, wherein the steam exiting the turbine ispreheated using heat from power generation equipment exhaust prior tobeing heated in the boiler system.
 10. The method of claim 8, wherein aduel fuel burner of a boiler system is used to combust the fuel and theboiler system heats the drying gas.
 11. The method of claim 10, whereinthe drying gas is heated by a heater burning gas and the system boiler.12. The method of claim 10, wherein the drying gas is heated by powergeneration equipment exhaust gas and the system boiler.
 13. The methodof claim 10, wherein, the fuel includes a mixture comprising biofuel,ambient air, and heated process air.
 14. The method of claim 9, whereinthe drying gas is heated by at least one of a heater burning gas, powergeneration equipment exhaust gas, and a system boiler.
 15. The method ofclaim 8, wherein reducing the moisture content of the at least partiallysaturated gas is performed using a condenser operable to receive waterat a first temperature and output the water at a second temperaturehigher than the first temperature, and wherein the water reduces thetemperature of the at least partially saturated gas.
 16. The method ofclaim 8, wherein combusting the fuel produces combusted gas having ashand a moisture content, and further comprising: reducing the moisturecontent of the combusted gas using a condenser, the condenser operableto receive water at a first temperature and output the water at a secondtemperature higher than the first temperature, and wherein the waterreduces the temperature of the combusted gas; discharging the reducedmoisture combusted gas; and separating the ash from the combusted gas.17. A system for generating electricity by using fuel produced fromprocessing dewatered sludge into a biofuel, the system comprising: adryer operable to: receive a drying gas; receive sludge; and reduce themoisture content of the sludge in the presence of the drying gas,thereby forming a biofuel comprising dried powder and an at leastpartially saturated gas; wherein the drying gas breaks down the sludgeand absorbs at least a portion of the moisture content of the sludge toform into a biofuel, the biofuel comprising dried powder, and an atleast partially saturated gas; a boiler operable to combust the biofuel;and a condenser operable to reduce a moisture content of the at leastpartially saturated gas by reducing a temperature of the at leastpartially saturated gas to form a reduced-moisture gas; and a diverteroperable to vent a volume of reduced-moisture gas based on a volume ofmoisture contained in the sludge introduced into the system.
 18. Thesystem of claim 17, further comprising a series of heat exchangersincorporated into the boiler system to transfer heat to at least one ofa turbine and the dryer.
 19. A method for producing electricity fromdewatered sludge in a treatment system, the method comprising: reducingmoisture content of a dewatered sludge by breaking the dewatered sludgeinto biofuel in the presence of a drying gas, wherein the drying gasabsorbs at least a portion of the moisture content of the dewateredsludge to form at least partially saturated gas; separating the biofuelfrom the at least partially saturated gas; combusting the biofuel toproduce at least one of a drying gas for use in the drying process andsteam for use in a turbine;
 20. The method of claim 19, furthercomprising: reducing a moisture content of the at least partiallysaturated gas by reducing a temperature of the at least partiallysaturated gas to below its dew point in order to form a reduced-moisturegas; and heating a portion of the reduced-moisture gas to generate thedrying gas; recirculating at least a portion of the drying gas bydirecting it to the dryer, wherein upon exiting the dryer it becomespartially saturated gas.